This description relates to electric power distribution systems, and more particularly to a combined grounding device and testing tool for use in an electric power distribution system.
In power distribution systems, high-voltage separable connectors interconnect various electrical equipment, such as transformers, switchgear, distribution cables, and the like. These connectors typically have an elbow component that mates with a bushing component.
The electrical equipment often needs to be grounded. For example, the electrical equipment must be grounded for repair or servicing, or when being moved to reconfigure or isolate parts of the system. In this case, a grounding device (e.g., a grounding elbow) is typically used to provide a visible ground.
A grounding and testing device for power distribution systems includes an electrically insulated housing with a bore that extends from an aperture at a front of the housing towards a rear of the housing. An electrical contact is disposed at least partially within the bore, and the bore, the aperture, and the contact are adapted to mate with a bushing. A current interrupter, such as a current limiting fuse, is electrically connected between the contact and a grounding cable. An annunciator is connected to the current interrupter such that the annunciator provides an indication when a current flows through the current interrupter. A lead is also electrically connected to the contact to provide a connection point for a permanent ground connection.
The grounding and testing device can reduce the forces that can occur when someone accidentally, or otherwise, closes a grounding device in on an energized system. For example, if a conventional 200 A grounding elbow is closed in on an energized part of a system that has more than 10,000 amps available, the fault current can cause arcing and can result in forces capable of propelling parts. One instance in which more than 10,000 amps would be available is in a 600 A portion of the system, which is rated at 25,000 amps. However, in the grounding and testing device described, the current interrupter may be designed or chosen to control both the peak current and the fault current duration to levels that are barely detectable, thereby reducing or eliminating these responses.
Implementations of the grounding and testing device may include one or more of the following features. For example, the electrical contact may be an electrically conductive rod. Alternatively, the electrical contact may be an annular ring located near the rear of the housing. The contact may extend along an axis of the bore through the rear of the housing. The device may include an electrically conductive connector connected to a portion of the contact that extends through the rear of the housing. The lead and the current interrupter may be connected to the contact by the connector. Alternatively, the current interrupter may be connected between the torque limiting head and the eye. The connector may be connected to the contact such that the contact can be rotated without rotating the connector.
Also, an eye may be connected to a portion of the rod extending through the rear of the housing to permit manipulation of the device using a hotstick. A torque limiting head may connect the eye to the contact. A tip of the contact may be designed to engage an internal nut of a load reducing tap plug.
In addition, the bore may be conical in shape with an annular locking ring formed near the rear of housing. The bore, the aperture, and the contact may be adapted to mate with a bushing having a 200 A interface.
Further, a web may be placed on the front of the housing for sealing a connection between the housing and a bushing.
In general, the device may be used to test and ground electrical equipment in a power distribution system by connecting grounding cable to ground and determining if the annunciator indicates that current has flowed through the current interrupter. A permanent ground connection is attached to the lead if the annunciator does not indicate that a current has flowed through the current interrupter.
The described grounding and testing device has particular application for an electrical connection of an underground power distribution system that uses a 600 A separable connector with a 200 A load reducing tap plug (LRTP), where the connector and the LRTP are rated in the 15-35 KV range. However, the device can also be designed for other connections at other voltages.
The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.